I have taken a look how exports are handled in PP 2010.  Although you are using P6, I believe the same events happen between both versions.  Exporting as a Wavefront object, you are given an option to create a morph target with no world translation, which means you should be able to apply your morph target while your model is in any pose and position.  However, saving in 3ds format will no give you such an option.  The actual selection box is entirely grayed out.  This may be the root of your problem.  Have you tried Wavefront OBJ format to create your morph target?